This invention relates generally to primary/secondary surge protection devices for protecting telephone communications related equipment from power and transient surges. More particularly, the present invention relates to an improved primary/secondary surge protector circuit for protecting telecommunication equipment from power and transient surges occurring on the tip and/or ring conductors of transmission lines connected thereto. Specifically, the primary/secondary surge protector circuit of the instant invention includes fusible links of a unique construction connected in series with a primary voltage suppressor formed as a single unit on a printed circuit board.
As is generally well-known to those skilled in the telecommunications industry, modern telecommunications equipment is susceptible to transient surges such as those caused by lightning strikes and other voltage surges on the transmission lines. Accordingly, primary surge protector circuits are known in the prior art which have been provided for connection to the incoming transmission lines so as to be normally non-conductive but are rendered conductive when a voltage surge exceeds a predetermined breakdown voltage (e.g., 250 V) for protecting the equipment. However, it is also known that voltage surges on the transmission lines which are well below the breakdown voltage of the primary surge protector circuit may nevertheless create possible damage to the equipment. Thus, telecommunication equipment manufacturers have also typically provided some type of secondary surge protection in conjunction with the primary surge protector circuits.
As is shown in FIG. 1, a prior art primary/secondary surge protector circuit includes a primary protector portion and a secondary protector portion. The primary protector portion is comprised of a primary voltage suppressor and a pair of bridle wires connected in series with the opposite ends of the voltage suppressor which are mounted on a printed circuit board. The bridle wires are either short pieces of gauged wire (e.g., #28 AWG size or less) or a fuse element. The bridle wires are required in order to meet or pass the primary test according to the specification set forth by UL Standards 497 and 497A. However, the use of the bridle wires in the form of short wires or fuse elements mounted on the printed circuit board has the disadvantages of increasing space requirements and costs. In addition, the bridle wires require the additional task of installation or assembly, thereby increasing manufacturing costs.
In view of these problems, the inventors have developed a way of replacing the short wires or fuse elements with fusible links consisting of tip and ring conductive traces of a unique construction formed on the printed circuit board.
Accordingly, it is a general object of the present invention to provide an improved primary/secondary surge protector circuit for protecting telecommunication equipment from power and transient surges which is relatively simple and economical to manufacture and assemble.
It is an object of the present invention to provide an improved primary/secondary surge protector circuit which meets the specifications set forth by UL Standards 497 and 497A.
It is still another object of the present invention to provide an improved primary/secondary surge protector circuit which includes fusible links of a unique construction connected in series with a primary voltage suppressor formed as a single unit on a printed circuit board in order to pass the primary test of the UL Standards 497 and 497A.
It is still yet another object of the present invention to provide an improved primary/secondary surge protector circuit which is characterized by a design wherein fusible links consisting of tip and ring conductive traces of a unique construction are formed on a printed circuit board.
In a preferred embodiment of the present invention, there is provided a primary/secondary surge protector circuit for protecting telecommunications equipment and the like from power and transient surges which includes a printed circuit board and a surge protector circuit. The surge protector circuit is mounted on the printed circuit board. The printed circuit board has at least one tip conductor trace formed on its top surface and extending between an input tip terminal pin and a first internal node and has at least one ring conductive trace formed on its top surface and extending between an input ring terminal pin and a second internal node.
The surge protector circuit includes a voltage suppressor operative connected to the tip conductive trace at the first node and to the ring conductive trace at the second node. The tip and ring conductive traces define fusible links which are open when an excessive current is passed therethrough.